The present invention relates to the apparatus for measuring the oxygen quantity in objects such as the cerebral tissues of a human body or an animal. The invention especially relates to the apparatus for measuring the oxygenation of hemoglobin in blood and of cytochrome in cells by detecting those through electromagnetic waves.
In general, in diagnosing the function of a body organ such as the cerebral tissues, the fundamental and important parameters to measure are the oxygen quantity in the body organ and the organ's utilization of oxygen. Supplying body organs with a sufficient quantity of oxygen is indispensable for the growth ability of fetuses and new-born infants. If the supply of oxygen to a fetus is insufficient, the probability that the fetus will not survive or that the new-born infant will die is high. Even if the new-born infant lives, however, serious problems in body organs may remain as sequela. The insufficiency of oxygen affects every body organ, but especially causes serious damage in the cerebral tissues.
To examine the oxygen quantity in body organs readily and at the early stage of illness, an examination apparatus disclosed in U.S. Pat. No. 4,281,645 patented on Aug. 4, 1981 has been developed. In this kind of examination apparatus, the variation of oxygen quantity in body organs, especially in the brain, is measured through the absorption spectrum of near infrared light. The absorption is caused by the hemoglobin which is an oxygen-carrying medium in blood and the cytochrome a, a.sub.3 which performs oxydation-reduction reaction in cells. As shown in FIG. 1(a), the absorption spectra of near infrared light (700 to 1300 nm), .alpha..sub.HbO2 and .alpha..sub.Hb by oxygenated hemoglobin (HbO.sub.2) and disoxygenated hemoglobin (Hb), respectively, are different from each other. And as shown in FIG. 1(b), the absorption spectra of .alpha..sub.CyO2 and .alpha..sub.Cy by oxidized cytochrome a, a.sub.3 (CyO.sub.2) and reduced cytochrome a, a.sub.3 (Cy), respectively, are different from each other. This examination apparatus utilizes the above-described absorption spectra of near infrared light. Four near infrared light rays with different wavelengths, .lambda..sub.1, .lambda..sub.2, .lambda..sub.3 and .lambda..sub.4 (e.g. 775 nm, 800 nm, 825 nm and 850 nm) are applied to one side of the patient's head with a time-sharing method and the transmission light rays from the opposite side of the head are in turn detected. By processing these four detected light rays with the prescribed calculation program the density variations of oxygenated hemoglobin (HbO.sub.2), disoxygenated hemoglobin (Hb), oxidized cytochrome a, a.sub.3 (CyO.sub.2) and reduced cytochrome a, a.sub.3 (Cy) are calculated. These parameters, in turn, determine the variation of cerebral oxygen quantity.
FIG. 2 shows a system outline of the above-described conventional examination apparatus 45. The conventional examination apparatus 45 includes; light sources such as laser diodes LD1 to LD4 which emit four near infrared light rays with different wavelengths of .lambda..sub.1, .lambda..sub.2, .lambda..sub.3 and .lambda..sub.4, respectively; a light source control device 55 which controls output timing of the light sources LD1 to LD4; optical fibers 50-1 to 50-4 which introduces near infrared light rays emitted by the light sources LD1 to LD4 to a patient's head 40; an illumination-side fixture 51 which bundles and holds end portions of the optical fibers 50-1 to 50-4; a detection-side fixture 52 which is fitted to the prescribed position of the opposite side of the patient's head 40; an optical fiber 53 which is held by the detection-side fixture 52 and introduces transmitted near infrared light from the patient's head 40; a transmission light detection device 54 which measures transmission quantity of near infrared light by counting photons of near infrared light introduced by the optical fiber 53; and a computer system 56 which controls the total examination apparatus and determines the variation of oxygen quantity in cerebral tissues being based on the transmission quantity of near infrared light.
The computer system 56 is equipped with a processor 62, a memory 63, output devices 64 such as a display and a printer, and an input device 65 such as a keyboard, and these devices are connected to each other by a system bus 66. The light source control device 55 and the transmission light detection device 54 are connected to the system bus 66 as external I/O's.
The light source control device 55 receives instructions from the computer system 56 and drives the light sources LD1 to LD4 by respective driving signals ACT1 to ACT4 as shown in FIGS. 3(a) to 3(d). As shown in FIG. 3 one measuring period M.sub.k (k=1, 2, . . . ) consists of N cycles of CYl to CYn. At a phase .phi.nl in an arbitrary cycle CYn, no light source of LD1 to LD4 is driven and therefore the patient's head 40 is not illuminated by the near infrared light from the light sources LD1 to LD4. At the phase .phi.n2 the light source LD1 is driven and the near infrared light with the wavelength of, for example, 775 nm is emitted from it. In the same manner, at the phase .phi.n3 the light source LD2 is driven and the near infrared light with the wavelength of, for example, 800 nm is emitted from it; at the phase .phi.n4 the light source LD3 is driven and the near infrared light with the wavelength of, for example, 825 nm is emitted from it; and at the phase .phi.n5 the light source LD4 is driven and the near infrared light with the wavelength of, for example, 850 nm is emitted from it. In this manner the light source control device 55 drives the light sources LD1 to LD4 sequentially with a time-sharing method.
Referring again to FIG. 5, the transmission light detection device 54 is equipped with a filter 57 which adjusts the quantity of near infrared light outputted to lenses 70 and 71 from the optical fiber 53; a photomultiplier tube 58 which converts the light from the filter 57 into pulse current and outputs it; an amplifier 59 which amplifies the pulse current from the photomultiplier tube 58; an amplitude discriminator 60 which eliminates the pulse current from the amplifier 59 whose amplitude is smaller than the prescribed threshold value; a multi-channel photon-counter 61 which detects photon frequency in every channel; a detection controller 67 which controls detection periods of the multi-channel photon-counter 61; and a temperature controller 68 which controls the temperature of a cooler 69 containing the photomultiplier tube 58.
To use the above-described examination apparatus, the illumination-side fixture and the detection-side fixture are firmly fitted to the prescribed positions of the patient's head 40 by using tape or the like. Once fitted the light sources LD1 to LD4 are driven by the light source control device 55 as shown in FIGS. 3(a) to 3(d), respectively, so that the four near infrared light rays with different wavelengths are emitted from the light sources LD1 to LD4 sequentially with the time-sharing method, and the light rays are introduced by the optical fibers 50-1 to 50-4 to the patient's head 40. As bones and soft tissues in the patient's head 40 are transparent to the near infrared light, the near infrared light is partially absorbed by hemoglobin in blood and cytochrome a, a.sub.3 in cells and outputted to the optical fiber 53. The optical fiber 53 introduces the light to the transmission light detection device 54. At the phase .phi.nl no light source of LD1 to LD4 is driven, and therefore the transmission light detection device 54 detects dark light.
The photomultiplier tube 58 in the transmission light detection device 54 is used with a photon-counting device that has high sensitivity and operates at high response speed. The output pulse current from the photomultiplier tube 58 is sent to the amplitude discriminator 60 through the amplifier 59. The amplitude discriminator 60 eliminates the noise component whose amplitude is smaller than the prescribed amplitude threshold and sends only the signal pulse to the multi-channel photon-counter 61. The multi-channel photon-counter 61 detects photons only in the periods T.sub.o. The periods T.sub.o are synchronized with the driving signals ACT1 to ACT4 for the respective light sources LD1 to LD4 as shown in FIGS. 3(a) to 3(d) by a control signal CTL as shown in FIG. 3(e ). The control signal CTL is generated by the detection controller 67. The multi-channel photon-counter then counts detected photons of every light with each wavelength sent from the optical fiber 53. The transmission data of every near infrared light with each wavelength are obtained through the abovedescribed procedure.
That is, as shown in FIGS. 3(a) to 3(e), at the phase .phi.nl in the cycle CYn of light source control device 55 no light source of LD1 to LD4 is driven, therefore the dark light data d are counted by the transmission light detection device 54. At the phases .phi.n2 to .phi.n5 the light sources LD1 to LD4 are sequentially driven with the time-sharing method and the transmission light detection device 54 sequentially counts the transmission data t.sub..lambda.z, t.sub..lambda.2, t.sub..lambda.3 and t.sub..lambda.4 of the respective near infrared light rays with different wavelengths .lambda..sub.1, .lambda..sub.2, .lambda..sub.3 and .lambda..sub.4.
The counting of the dark light data d and the transmission data t.sub..lambda.1, t.sub..lambda.2, t.sub..lambda.3 and t.sub..lambda.4 which is sequentially performed in the cycle CYn, is continued N times from CYl to CYn. That is, one measuring period M.sub.k (k=1, 2, . . . ) includes N cycles. A concrete example is as follows; if one cycle is 200 .mu.sec and N is 10000, the measuring period M.sub.k becomes 2 sec. At the time of finishing of One measuring period M.sub.k, the counting result of the dark light data ##EQU1## and the counting results of the transmission data T.sub..lambda.1, T.sub..lambda.2, T.sub..lambda.3 and T.sub..lambda.4 ##EQU2## are transferred to the computer system 56 and stored in the memory 63.
The processor 62 performs the ,subtraction of the dark light component by using the combination of the transmission data and the dark data (T.sub..lambda.1, T.sub..lambda.2, T.sub.80 3, T.sub..lambda.4, D)M.sub.k being stored in the memory 63 after one measuring period M.sub.k and the combination of those (T.sub..lambda.1, T.sub..lambda.2, T.sub..lambda.3, T.sub..lambda.4, D)M.sub.o at the start of measuring, and calculates the variation rates of the transmission light .DELTA.T.sub..lambda.1, .DELTA.T.sub..lambda.2, .DELTA.T.sub..lambda.3 and .DELTA.T.sub..lambda.4. That is, the variation rates of the transmission light .DELTA.T.sub..lambda.1, .DELTA.T.sub..lambda.2, .DELTA.T.sub..DELTA.3 and .DELTA.T.sub..lambda.4 are calculated as: EQU .DELTA.T.sub..lambda.j =log[(T.sub..lambda.j -D).sub.mk /(T.sub..lambda.j -D).sub.Mo ](j=1 to 4). (1)
The use of logarithm in the above calculation of .DELTA.T.sub..lambda.j is to express the variation as an optical density.
Using the above-calculated variation rates of the transmission light .DELTA.T.sub..lambda.1, .DELTA.T.sub..lambda.2, .DELTA.T.sub..DELTA.3 and .DELTA.T.sub..lambda.4, density variations of oxygenated hemoglobin (HbO.sub.2), disoxygenated hemoglobin (Hb), oxidized cytochrome a, a.sub.3 (CyO.sub.2) and reduced cytochrome a, a.sub.3 which are expressed as .DELTA.X.sub.HbO.sbsb.2 .DELTA.X.sub.ab, .DELTA.X.sub.CyO.sbsb.2 and .DELTA.X.sub.cy, respectively, can be determined. That is, each of density variations of .DELTA.X.sub.HbO.sbsb.2 .DELTA.X.sub.Hb, .DELTA.X.sub.CyO.sbsb.2 and .DELTA.X.sub.cy is calculated as: ##EQU3## where .DELTA..sub.ij is an absorption coefficient of each component i (HbO.sub.2, Hb, CyO.sub.2, Cy) for each wavelength .lambda..sub.j (.lambda..sub.1, .lambda..sub.2, .lambda..sub.3, .lambda..sub.4) and is predetermined from FIGS. 1(a) and 1(b), and l is the length of the patient's head 40 along the travelling direction of the near infrared light.
As the above-detected density variation components, .DELTA.X.sub.Hbo.sbsb.2, .DELTA.X.sub.Hb, .DELTA.X.sub.CyO.sub.2 and .DELTA.X.sub.Cy, reflect the variation of oxygen quantity in the brain, the variation of oxygen quantity in the brain can be determined by outputting these detected results from the output device 64. The diagnosis is thus made based on these results.
The illumination-side fixture 51 and the detection-side fixture 52 of the foregoing examination apparatus hold the optical fibers 50-1 to 50-4 and the optical fiber 53, respectively, in such a manner that the fibers are perpendicular to the outer skin layer of the head 40 as shown in FIG. 2, in order to make the near infrared light perpendicularly incident on the head 40 and also make the transmission light perpendicularly incident on the optical fiber 53 so as to obtain maximum illumination efficiency and detection efficiency.
However, when the illumination-side fixture 51 and the detection-side fixture 52 are fitted to the head 40 in the actual use, the optical fibers (glass fibers) 50-1 to 50-4 and 53 which can just be bent to a comparatively large radius of curvature are required to be bent by prescribed degrees as shown in FIG. 2. And it is not easy to make these fixtures 51 and 52 firmly fit to the head 40. If the head 40 is moved in the midst of the measurement, the fitting positions of these fixtures are likely to be changed, resulting in a difficulty in performing an accurate measurement. Also with the structure of these fixtures, there exist limits in shortening the lengths of the optical fibers 50-1 to 50-4 and 53 in order to reduce transmission losses in the fibers of the near infrared light rays emitted from the light sources LD1 to LD4 or transmitted from the head 40.
It is necessary that the illumination-side fixture 51 and the detection-side fixture 52 hold the optical fibers 50-1 to 50-4 and the optical fiber 53 by prescribed lengths respectively, in order to always keep the optical fibers 50-1 to 50-4 and 53 perpendicular to the outer skin layer of the head 40. Therefore, the fixtures 51 and 52 become so large that they cannot be fitted easily to the head 40 by a tape for intercepting ambient light.
It is desired that the fixtures 51 and 52 can be assembled together opposite to each other as shown in FIG. 4 when they are stored, in the custody of, or used, in order to prevent that the contact surfaces to the object of the fixtures are damaged or stained when the examination apparatus is not in use, or in order to inspect the examination apparatus itself. But, the conventional fixtures 51 and 52 are not suitable for being assembled together opposite each other when they are stored, in the custody of, or used, because they hold the respective optical fibers 50-1 to 50-4 and 53 so that the optical fibers are perpendicular to the outer skin layer of the head 40.
On the other hand, the conventional examination apparatus 45 has another kind of problems in connection with the fixtures 51 and 52 as described in the following.
When the operator of the examination apparatus fits the illumination-side fixture 51 and the detection-side fixture 52 to the head 40 etc. of the object person or removes those from the head etc., he should confirm that the light sources LD1 to LD4 are not being driven and the photomultiplier tube 58 is not in the operating condition. The light sources LD1 to LD4 should not be driven in fitting or removing the fixtures to prevent the near infrared light rays from being emitted from the illumination-side fixture 51 to the outside. Also, the photomultiplier tube 58 should not be in the operating condition in that situation, because the photomultiplier tube is damaged when the detection-side fixture 52 is faced to an outside bright area.
However, the conventional examination apparatus has the problem that the operator fails to make the above-described confirmation or at least it is not easy for the operator to make the confirmation. This problem is originated from the fact that the illumination-side fixture 51 and the detection-side fixture 52 are connected to the end portions of the respective optical fibers 50-1 to 50-4 and 53, the end portions being far from the main body of the examination apparatus.
Another problem in the conventional apparatus is that as in general the fixtures 51 and 52 are comparatively small and have the same shape and color, it is confusing which is the illumination-side fixture or detection-side fixture.